The present invention relates generally to the field of radiation sensitive positive and negative photoresist compositions and particularly to compositions containing novolak resins together with naphthoquinone diazide sensitizing agents.
It is well known in the art to produce positive photoresist formulations such as those described in U.S. Pat. Nos. 3,666,473, 4,115,128 and 4,173,470. These include alkali-soluble phenol-formaldehyde novolak resins together with light-sensitive materials, usually a substituted naphthoquinone diazide compound. The resins and sensitizers are dissolved in an organic solvent or mixture of solvents and are applied as a thin film or coating to a substrate suitable for the particular application desired.
The novolak resin component of these photoresist formulations is soluble in alkaline aqueous solution, but the naphthoquinone sensitizer acts as a dissolution rate inhibitor with respect to the resin. Upon exposure of selected areas of the coated substrate to actinic radiation, however, the sensitizer undergoes a radiation induced structural transformation and the exposed areas of the coating are rendered more soluble than the unexposed areas.
The relief pattern of photoresist on substrate produced by the method described above is useful for various applications including, for example, as an exposure mask or a pattern such as is employed in the manufacture of miniaturized integrated electronic components.
In many industrial applications, particularly in the manufacture of miniaturized electronic components, a photoresist is required to provide a high degree of resolution for very small line and space widths (on the order of one micron or less).
The ability of a resist to reproduce very small dimensions, on the order of a micron or less, is extremely important in the production of large scale integrated circuits on silicon chips and similar components. Circuit density on such a chip can only be increased, assuming photolithography techniques are utilized, by increasing the resolution capabilities of the resist. Although negative photoresists, wherein the exposed areas of resist coating become insoluble and the unexposed areas are dissolved away by the developer, have been extensively used for this purpose by the semiconductor industry, positive photoresists have inherently higher resolution and are utilized as replacements for the negative resists.
This invention relates to a composition for stripping, thinning and cleaning cured and uncured photoresist compositions from substrates covered with such resins and to the stripping process using such compositions.
Both mechanical and chemical processes are known for the removal of the aforementioned resinous coatings from a substrate, but these processes leave much to be desired. If the cured coating is mechanically stripped as by scraping, the removal of the material is almost invariable accompanied by some physical damage. The use of certain chemical reagents or solvents, formerly employed, is unsatisfactory since they dissolve the cured resins either too slowly or incompletely or both, or they comprise the electrical reliability by leaving residual contaminants which are not completely removed by subsequent processing. A solvent or stripping solution which will both quickly and completely remove the aforementioned cured resins from the substrates without damage or contamination thereof is therefore needed.
Solvent compositions are known which may be used for thinning photoresist compositions, stripping undesired cured and uncured photoresist from wafers, removing undesired edge bead from spun photoresist wafers and cleaning related photoresist processing equipment. However, such compositions are generally extremely toxic, ecologically undesirable and/or are unpleasantly odorous.
The present invention seeks to solve the aforementioned disadvantages.
A positive working photoresist comprising propylene glycol alkyl ether acetate is described in U.S. patent application Ser. No. 619,468 filed June 11, 1984, as well as U.S. patent application Ser. No. 791,252, filed on Oct. 25, 1985, abandoned and which are incorporated herein by reference.
A positive working photosensitive composition comprising a mono C.sub.1 to C.sub.4 alkyl glycol ether of 1,2 propanediol is described in U.S. Ser. No. 742,063 filed June 6, 1985, abandoned and is incorporated herein by reference.
A positive working photosensitive composition comprising a mixture of propylene glycol alkyl ether acetate and propylene glycol alkyl ether is described in U.S. patent application Ser. No. 791,880, filed on even data herewith, abandoned and is incorporated herein by reference. Photoresist treating compositions containing only one of propylene glycol alkyl ether and propylene glycol alkyl ether acetate have a disadvantage. Propylene glycol monomethyl ether acetate (PGMEA) has an offensive odor to approximately one-half the people who came in contact with it. These are usually women. Propylene glycol monomethyl ether (PGME) is also offensive to approximately one-half the people who are exposed to it. These are usually men. However, those who find PGMEA offensive find PGME to have little or no odor. The reverse is also true, those who object to PGME find PGMEA to be pleasant or not objectionable. Mixtures of these solvents i.e. PGME/PGMEA (1:1) are not objectionable, or at least less objectionable to both groups of individuals. Based on these observations photoresist treating compositions using PGME/PGMEA mixtures form a class of reduced odor compositions.